Date of Award

2019

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Chemistry and Biochemistry

First Advisor

Alison Noble

Second Advisor

Niklas Hellgren

Abstract

Alkanethiolate self-assembled monolayers (SAMs) have been formed on zinc selenide (ZnSe) through adsorption from solution. Zinc selenide as a SAM-supporting substrate is of particular interest due to its transparency in the infrared region of the electromagnetic spectrum, enabling interfacial interactions at the substrate surface to be studied through transmission IR spectroscopy. In the past, mechanically polished, optical quality ZnSe surfaces have been used to support SAM formation. This surface, however, typically has a rms roughness around 40 nm, meaning it cannot support highly-ordered SAMs. In order to promote more consistent formation of highly-ordered SAM, a smoother supporting substrate is required. A significantly smoother ZnSe surface has be produced through physical vapor deposition (PVD) onto silicon substrates. The PVD-generated zinc selenide thin film exhibits the same IR transparency as the mechanically polished substrate, but with a rms roughness in the range of 2.7 ± 0.9 nm, which is over an order of magnitude improvement in surface roughness. The thin film ZnSe-SAM system was characterized through Fourier Transform Infrared (FTIR) spectroscopy, contact angle goniometry and x-ray photoelectron spectroscopy (XPS). In the XPS spectra, the shifts and relative intensities of Zn 2p, Se 3d, S 2p, and C 1s peaks when SAMs adsorbed to the surface have been used to show whether the SAM is physiosorbed or chemisorbed. A significant shift in the S 2s peak for a ZnSe film with SAMs compared to free thiol literature values, which is indicative of a change in chemical environment, provides evidence for chemisorption of thiolate SAMs to the ZnSe thin film.

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